Interpretive Summary: Some conventional plastics are produced from petroleum-based feedstocks and persist in the environment for years. Biodegradable polymers, such as polycaprolactone (PCL), can be degraded in the environment by microorganisms, oxidation and hydrolysis. Biodegradable polymers can be utilized for packaging materials, hygiene products, disposable consumer goods, and agricultural products. The cost of PCL can be reduced by blending agricultural materials, such as wheat gluten (WG), into composite materials with appropriate mechanical properties. The manuscript reports on the formation of a polymer composite composed of PCL and WG fabricated by twin-screw extrusion and injection molding. The data show that there is some adhesion between PCL and WG in the composites indicating that WG is not an inert filler and contributes to the overall mechanical properties of the composite. The composites are biodegradable and competitive in cost with comparable non-sustainable petroleum-based products currently in the marketplace. The current study presents a new way to utilize agricultural materials for the future profitability of the agriculture industry.

Technical Abstract:
Wheat gluten (WG) was incorporated into poly(caprolactone) (PCL) up to 50% w/w as a filler to form a biodegradable polymer composite. Microscopic examination showed a well-dispersed particle-matrix system. The composite was evaluated for tensile properties. The tensile strength of the composite decreased linearly with increasing wheat gluten content from 20 MPa (0% WG) to 6 MPa (50% WG). However, the decreases in tensile strength did not fit the Nicolais-Narkis model indicating that some adhesion between WG and PCL occurred. High elongation (>900%) was observed in PCL-WG composites with up to 20% WG which decreased to 400% at 35% WG and finally to less than 100% at 40-50% WG. There was a particle-induced transition at a calculated critical volume of 0.3 corresponding to 30% WG by weight to PCL.